1. Field of the Invention
The present invention relates to a novel polymeric compound, a resist composition containing the polymeric compound, and a method of forming a resist pattern that uses the resist composition.
Priority is claimed on Japanese Patent Application No. 2011-257859, filed Nov. 25, 2011, the content of which is incorporated herein by reference.
2. Description of Related Art
In lithography techniques, for example, a resist film composed of a resist material is formed on a substrate, and the resist film is subjected to selective exposure of radial rays such as light or an electron beam through a mask having a predetermined pattern formed therein, followed by development, thereby forming a resist pattern having a predetermined shape on the resist film.
A resist material in which the exposed portions become soluble in a developing solution is called a positive-type, and a resist material in which the exposed portions become insoluble in a developing solution is called a negative-type.
In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of pattern miniaturization.
Typically, these pattern miniaturization techniques involve shortening the wavelength (and increasing the energy) of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays KrF excimer lasers and ArF excimer lasers are starting to be introduced in the mass production of semiconductor elements. Furthermore, research is also being conducted into lithography techniques that use an exposure light source having a shorter wavelength (and a higher energy level) than these excimer lasers, such as electron beam (EB), extreme ultraviolet radiation (EUV) and X-ray.
Resist materials for use with these types of exposure light sources require lithography properties such as a high resolution capable of reproducing patterns of minute dimensions, and a high level of sensitivity to these types of exposure light sources.
As a resist material that satisfies these conditions, a chemically amplified resist composition is used, which includes a base component that exhibits changed solubility in a developing solution under the action of acid, and an acid generator component that generates acid upon exposure.
For example, in the case where the developing solution is an alkali developing solution (alkali developing process), a positive-type chemically amplified resist composition containing a resin component (base resin) which exhibits increased solubility in an alkali developing solution under the action of acid, and an acid generator component is generally used. If the resist film formed using this resist composition is selectively exposed during formation of a resist pattern, then acid is generated from the acid generator component within the exposed portions, and the action of this acid causes an increase in the solubility of the resin component in an alkali developing solution, making the exposed portions soluble in the alkali developing solution. The unexposed portions remain to form a positive-type resist pattern. The base resin exhibits increased polarity under the action of acid, thereby exhibiting increased solubility in an alkali developing solution, whereas the solubility in an organic solvent decreases. Accordingly, if a process that uses a developing solution containing an organic solvent (an organic developing solution) is employed (hereafter, this process is referred to as a “solvent developing process” or “negative-type developing process”) instead of an alkali developing process, then within the exposed portions of the resist film, the solubility in the organic developing solution decreases relatively. As a result, during the solvent developing process, the unexposed portions of the resist film are dissolved in the organic developing solution and removed, whereas the exposed portions remain as a pattern, resulting in the formation of a negative-type resist pattern. For example, Patent Document 1 proposes a negative-type developing process and a resist composition for use within the process.
Currently, resins that contain structural units derived from (meth)acrylate esters within the main chain (acrylic resins) are widely used as base resins for resist compositions that use ArF excimer laser lithography or the like, as they exhibit excellent transparency in the vicinity of 193 nm (for example, see Patent Document 2).
In order to improve various lithography properties, the base resin usually contains a plurality of structural units. For example, in the case of a resin component that exhibits higher polarity under the action of acid, a base resin is typically used that includes a plurality of structural units, including a structural unit having an acid-decomposable group that exhibits increased polarity upon decomposition under the action of the acid generated from the acid generator component, a structural unit having a polar group such as a hydroxyl group, and a structural unit having a lactone structure.
In particular, structural units having a polar group are widely used, since they improve the compatibility with an alkali developing solution, and contribute to favorable improvements in the resolution.
Recently, base resins having a structural unit containing an imide group have also been proposed (for example, see Patent Document 3). These base resins contribute to improvements in the resolution and mask reproducibility and the like.